Field
Integrated circuit structures.
Description of Related Art
Integrated circuit structures generally include devices such as field effect transistors formed in or on a semiconductor substrate in combination with a multi-level interconnect structure with connections between different ones of the devices. A representative multi-level interconnect structure includes one or more arrays or levels of wiring lines to provide connections to and between devices. Closely spaced, generally parallel wiring lines, can provide undesirable level of capacitive coupling, particularly, for higher data transmission rates through the wiring lines. Such capacitive coupling can slow data transmission rates and increase energy consumption in a manner that can limit the performance of the integrated circuits.
One effort to reduce an undesirable level of capacitive coupling between adjacent wiring lines is modifying the dielectric material that separates the wiring lines. Specifically, efforts have been made to replace dielectric materials that have relatively high dielectric constants with materials having lower dielectric constants. Using air as a dielectric by forming, for example, air gaps between adjacent metal lines is one strategy. However, one issue surrounding the use of air gaps is unlanded vias. When conductive vias are misaligned with respect to wiring lines at, for example, a level below and land in an air gap, such misaligned vias reduce shorting margin or, in the worst case, can short adjacent lines. Undesired metal deposition in the air gap through an unlanded via also impacts interconnect reliability. Accordingly, efforts directed at introducing air gapped layers use masks to prevent formation of air gaps where vias are present. Use of masks, however, limits the implementation of air gaps, particularly, in lower interconnect levels where via density tends to be higher or in areas involving tight pitches.